How to join a match by IP address in CS:GO?
There are two methods, you can open up the console in game and type "connect 127.0.0.1:27015" where 127.0.0.1:27015 is your IP address and port number. You have to have the console enabled for this option to work. Usually it's by hitting escape to bring you to the menu and then pressing the tilde (~) key.
Or you can add the server to favourites from in game or out of game through steam. You do this by bringing up the server window, and clicking on the Add A Server button and it will ask you to add the server address to the window and then it will always be there!